Sleep
Terms,
Definitions and Abbreviations

Abdominal
Movement - In diagnostic sleep studies, abdominal movement
is recorded. This is one of the measures of respiratory effort, reflecting
movement of the diaphragm.

Advanced Sleep Phase Syndrome(ASPS)
- Phases of the daily sleep/wake cycle are advanced with respect to clock
time. This is classified as a circadian rhythm disorder. The sleep phase
occurs well ahead of the conventional bedtime and the tendency is to wake
up too early.

Alpha
rhythm - EEG oscillations, prominent over the occipital cortex, with
a frequency of 8-13 Hz in adults; indicative
of the awake state; present in most, but not all, normal individuals; most consistent and predominant during relaxed wakefulness.

Alpha
intrusion - brief occurrence of alpha activity during a stage of sleep.

Ambulatory
Monitor - Portable system used to record (continuously) multiple physiological
variables during sleep.

Apnea
- Literally means "no breath", the cessation of airflow at the nostrils and mouth for at least 10
seconds.

Apnea
index (AI) - A measure of the severity of sleep apnea; the number of apnea events per hour.

Basic
Sleep Cycle - progression through orderly succession
of sleep states and stages. For the healthy adult, the first cycle is begins
by going from wakefulness to non-REM sleep. The first REM period follows
the first period of non-REM sleep, and the two sleep states continue to
alternate throughout the night with an average period of about 90 minutes.
A night of normal human sleep usually consists of 4-6 non-REM/REM sleep
cycles.

Benzodiazepines - developed in the 1950's,
this class of compounds tranquilize and sedates.

Bi-Level - Bi-level pressure device
used to treat sleep apnea. The "bi" refers to two pressures: a lower pressure for exhalation and a higher pressure for inhalation. Bi-Level
machines are more expensive than a standard CPAP, but some patients tolerate
it better because they can exhale comfortably against the constant inhalation
pressure. (Sometimes called Bi-PAP, but that is a trademark name
of one system)

Biological
Clock - term for the brain process causing us to have 24-hour fluctuations
in body temperature, hormone secretion, and other bodily activities. The
most important function fosters the daily alternation of sleep and wakefulness.
The biological clock is found in a pair of tiny bilateral brain areas called
the suprachiasmatic nuclei.

Body
Position - four positions are identified which a patient may be sleeping;
back, left side, right side or abdomen. The time spent sleeping in each
position and the number of respiratory events in a particular position are
tabulated.

Bradycardia
- heart rhythm with a rate lower than 60 beats per minute in an adult.

Cataplexy
- sudden, dramatic decrement in muscle tone and loss of deep reflexes that
leads to muscle weakness, paralysis, or postural collapse. Usually caused by outburst of emotion: laughter, startle, or sudden physical exercise;
one of the tetrad of symptoms of narcolepsy.

Central
apnea - absence of airflow and inspiratory effort; apnea caused by irregularity in the brain's control of breathing.

Chronotherapy
- treatment for circadian rhythm sleep disorder by systemically changing
sleeping and waking times to reset the biological clock.

Circadian rhythm - innate, daily, fluctuation
of behavioral and physiological functions, including sleep waking, generally
tied to the 24 hour day-night cycle but sometimes to a different (e.g.,
23 or 25 hour) periodicity when light/dark and other time cues are removed.

Compliance
- adhering to or conforming with a regimen of treatment such as CPAP

CPAP
- Continuous Positive Airway Pressure;
the device used to treat sleep apnea by sending positive airway pressure
at a constant, continuous pressure to help keep an open airway, allowing
the patient to breathe normally through his/her nose and airway

CPAP
Pressure - pressure needed to maintain an open airway in a sleep apnea
patient treated with CPAP, expressed in centimeters of water (cm H20). The
positive pressure can range from 5 - 20 cm H20. Different patients require
different pressures. The value is determined in a CPAP titration study.

Delayed
sleep phase - A condition occurring when the clock hour at which sleep
normally occurs is moved back in time in a given, 24 hour sleep-wake cycle.
The result is a temporarily displaced (delayed) occurrence of sleep within
the 24 hour cycle.

Diagnostic
Sleep Study - monitoring of several physiological activities in a sleeping
individual. Usually performed to determine the absence or presence of a
specific sleep disorder. The sleep study can occur in a sleep disorders
center or in a patient's home with portable recording equipment.

Diaphragm
- large, concave muscle attached to the rib cage at bottom of the chest
(top of the abdomen). Inhalation occurs when diaphragm contracts. Exhalation
is passive as the muscle relaxes.

Diurnal
- active and wakeful in the daytime versus active in the nighttime

DME - Durable Medical Equipment. Equipment
such as wheelchairs and walkers which are prescribed for use by or on the
order of a physician, also includes CPAP and BI-Level machines.

Electroencephalogram
(EEG) - recording through the scalp of electrical potentials from the
brain and the changes in these potentials. The EEG is one of the three basic
variables (along with the EOG & EMG) used to score sleep stages and
waking. Surface electrodes are used to record sleep in humans, recording
potential differences between brain regions and a neutral reference point,
or between brain regions.

Electromyogram
(EMG) - recording of electrical activity from the muscular system; in
sleep recording, synonymous with resting muscle activity or potential. The
chin EMG, along with EEG and EOG, is one of the three basic variables used
to score sleep stages and waking. Surface electrodes are used to record
sleep in humans, measuring activity from the submental or masseter muscles.
These reflect the changes in resting muscle activity.
During REM sleep the chin/cheek EMG is tonically inhibited.

Electro-oculogram
(EOG) - recording of voltage changes resulting from shifts in position
of the eyeball-possible because each globe is a positive (anterior) and
negative (posterior) dipole; along with the EEG and the EMG, one of the
three basic variables used to score sleep stages and waking. Human sleep
recordings utilize surface electrodes placed near the eyes to record the
movement of the eyeballs. Rapid eye movements in sleep indicate a certain
stage of sleep ( usually REM sleep).

ENT
- Ear, Nose and Throat. A doctor
specializing in diseases of the Ear, Nose and Throat. These specialists often do surgery as well, and may be referred
to as an ENT surgeon.

Epidemiology
- Scientific discipline studying the incidence, distribution, and control
of disease in a population. Includes the study of factors affecting the
progress of an illness, and, in the case of many chronic diseases, their
natural history.

Epoch
- A standard 30 second duration of the sleep recording that is assigned
a sleep stage designation; for special purposes, occasionally longer or
shorter epochs are scored.

Epworth
Sleepiness Scale - index of sleep propensity during the day as perceived
by patients, and derived from the answers to 8 questions.

Esophageal
Pressure - measurement used to determine respiratory effort and by inference,
airway resistance. Considered an invasive measure, generally used only in
polysomnographic testing, conducted in sleep disorders centers.

Excessive
daytime sleepiness or somnolence (EDS) - subjective report of difficulty in staying awake, accompanied by
a ready entrance into sleep when the individual is sedentary

Expiratory
Phase - air is expelled during this phase of the breathing cycle

Fatigue
- feeling of tiredness or weariness usually associated with performance
decrements

Flattening
Index - number indicating the amount of airflow limitation caused by
partial closure of the upper airway. 0.3 indicates an open airway, 0.15
is mildly obstructed, 0.1 is severely limited airflow, and 0.0 reflects
a totally closed airway. Flattening
Index is used to identify the condition known as Upper Airway Resistance
Syndrome (UARS), and is continuously recorded in both diagnostic sleep studies
and CPAP titrations.

Flow
Limitation - the partial closure of the upper airway impeding the flow
of air into the lungs.

Forbidden
Zone - the period of strongest clock-dependent alerting, usually in
the evening. Prevents falling asleep.

Fragmentation (pertaining to Sleep Architecture)
- interruption of a sleep stage as a result of the appearance of a lighter
stage, or to the occurrence of wakefulness, which leads to disrupted non-REM-REM
sleep cycles.

GABA
(Gamma-Amniobutyric Acid) - major neurotransmitter in the brain, which
is considered to be involved in muscle relaxation, sleep, diminished emotional
reaction and sedation.

Gastroesphageal
Reflux Disease (GERD) - flow of stomach acid upwards into the esophagus
that can cause arousals and disrupt sleep.

Genioglossus
tongue advancement - a possible surgical treatment used for sleep apnea
and/or snoring, improving the airway behind the base of the tongue. The
genioglossus, the main tongue muscle, relaxes during sleep, often allowing
the tongue to fall into the airway. The muscle attaches to the middle of
the lower jaw. A segment of bone containing this muscle is
pulled forward and stabilized, opening the airway space behind the tongue.

Habitual
Snorers - those who snore nearly every night

Heart
Rate or beats per minute (bpm) - pace/speed of the heart measured in
beats per minute. 60-80 is considered normal in adults.

Humidification
- moisture is added to the airflow as an adjunct to CPAP (Continuous Positive
Airway Pressure) therapy in treating obstructive sleep apnea (OSA). Humidification
can be added to the CPAP by diverting the airflow over or through a cool
or heated water reservoir (humidifier) to prevent the upper airway from
drying out.

Hyoid Suspension - a possible surgical
procedure sometimes used in the treatment of sleep apnea and/or snoring,
designed to improve the airway behind the base of the tongue. The hyoid
bone is located in the neck where some tongue muscles attach. The hyoid
bone is pulled forward in front of the voice box and can open the airway
space behind the tongue.

Hyperactivity - typical behavior in
a child with a sleep disorder which is causing lack of quality sleep

Laser
assisted uvulopalatoplasty (LAUP) - can eliminate or
decrease snoring but has not been shown to be effective in the treatment
of sleep apnea.

Leg
Movement - Leg movements are recorded in both diagnostic sleep studies
and titration studies.

Letter
of Medical Necessity (LMN) - certification by a physician that the prescribed
item(s) is/are medically indicated, reasonable and necessary with reference
to the standards of medical practice and treatment of a patient's condition

Light
Therapy - used in the treatment of SAD (Seasonal Affective Disorder)
and other conditions. Exposes the eyes to light of appropriate intensity
and duration and at the appropriate time of day to effect the timing, duration
and quality of sleep.

Limit-Setting
Sleep Disorder - disorder due to child’s difficulty in falling asleep
by delaying and refusing to go to bed

Linear
Sleepiness Rating Scale - measure of subjective sleepiness. The scale contains a horizontal line, 100 mm
in length - the right extreme is labeled "Very Sleepy" and the
left extreme is labeled "Very Wide Awake."

Macroglossia
- large tongue; usually a congenital disorder (present at birth)

Maxillofacial
- pertaining to the jaws and face.

Mandibular
Maxillary Osteotomy and Advancement (MMOA) - procedure developed for
patients with retrolingual obstruction, patients with retropalatal and retrolingual
obstruction who have not responded to CPAP and uvulopalatopharyngoplasty
(UPPP).

Melatonin
- hormone secreted by the brain’s pineal gland

Micro-arousal
- partial awakening from sleep

Micro-sleep
- period lasting up to a few seconds during which the polysomnogram suddenly
shifts from waking characteristics to sleep.

Mixed
(sleep) apnea - interruption in breathing during sleep beginning as
a central apnea then becoming an obstructive apnea.

Monocyclic
- a single major sleep period and a single major wake period in a 24-hour
day.

National
Commission on Sleep Disorders Research (NCSDR) - the commission (created
by the U.S. Congress in 1990) conducted a comprehensive study of the social
and economic impact of sleep disorders in America and made recommendations
based on its findings to the Congress in January 1993

Neurology
- branch of medicine that referring to the nervous system and its diseases

Neurotransmitters
- endogenuous chemical components that are released from axon terminals
of one neuron and transmit the signal to the next neuron by combining with
its receptor molecules. Neurotransmitters
important in the control of sleep and wakefulness include: norepinephrine,
serotonin, acetylcholine, dopamine, adrenaline and histamine.

Night
Terrors - also known as sleep terrors, or pavor nocturnus. Night terrors are characterized by an incomplete
arousal from slow wave sleep. If,
the individual is awakened during a night terror, he/she is usually confused
and does not remember details of the event. Night terrors are different from nightmares; if an individual is
awakened during a nightmare, he/she functions well and may have some recall
of the nightmare.

Nocturia
- excessive, often frequent, urination during the night

Nocturnal
- "Of the night;" pertaining to events happening during sleep
or the hours of darkness.

Nocturnal Confusion - episodes of delirium
and/or disorientation near or during nighttime sleep; often seen in victims
of Alzheimers Disease and more common in the elderly

Nocturnal sleep-related eating disorder
(NS-RED)- Getting up during the night and eating while sleepwalking.
No recall in the morning.

Nocturnal
Enuresis (Bedwetting) - urinating while asleep

Non-Invasive
- Medical procedure not penetrating the skin or a body cavity.

NREM
or non-REM sleep - characterized by slower and larger brain waves and
little or no dream behavior; quiet
sleep, slow-wave sleep; approximately
80% of sleep

NREM
Sleep Intrusion - brief period of NREM sleep patterns appearing in REM
sleep; a portion of NREM sleep not
appearing in its usual sleep cycle position

Obstructive
apnea - cessation of airflow (at least 10 seconds) in the presence of
continued inspiratory effort, cessation
of breathing during sleep, due to a mechanical obstruction, such as a semi-collapsed
trachea, tongue relaxed to back of the throat, or a large among of tissue
in the uvula area.

Obstructive
Hypopnea - periodic and partial closure of the throat during sleep resulting
in reduced air exchange at the level of the mouth and/or nostril.

Ondine's
Curse - the respiratory center in the brain is unable to stimulate breathing
in response to an increased amount of carbon dioxide in the blood. Ondine's Curse or central alveolar hypoventilation
typically worsens during sleep.

Optimum
Sleep - average amount of sleep needed every night by an individual.

Oxygen
Desaturation - less than normal amount of oxygen carried by hemoglobin
in the blood; values below 90% are
considered abnormal

Parasomnia
- an event happening during sleep, or induced or exacerbated by sleep, such
as sleepwalking or asthma; not a dyssomnia.

Paroxysmal
nocturnal dyspnea (PND) - respiratory distress and shortness of breath
due to pulmonary edema, appearing suddenly and often awakening the sleeping
individual.

Pathological
Sleep - abnormal sleep patterns.

Pavor
Nocturnus (Night Terrors) - See Night Terrors.

Perceptual
Disengagement - change in consciousness at the onset of sleep when environmental
stimuli are no longer perceived, and there is no longer any conscious, meaningful
interaction with the environment.

Periodic
Limb Movement Disorder - also known as periodic leg movements and nocturnal
myoclonus. Characterized by periodic episodes of repetitive and highly stereotyped
limb movements occuring during sleep. The movements are often associated
with a partial arousal or awakening; however, the patient is usually unaware
of the limb movements or frequent sleep disruption. Between the episodes, the legs are still. There
can be marked night-to-night variability in the number of movements or in
the existence of movements.

Pharynx
- area posterior to the nares and the oral cavity; passageway for air from the nasal cavity and/or the mouth to the
lungs via the larynx and the trachea, for food and liquids from the mouth
to the esophagus

Phase
advance - movement to a position earlier in the 24 hour sleep - wake
cycle of a period of sleep or wake; for example, a shift of the sleep phase
from 11 p.m. - 7 a.m. to 8 p.m. - 4 a.m.

Phase
delay - Phase delay is exactly the opposite of phase advance, i.e.,
a shift later in time.

Phasic
(Event/Activity) - brain, muscle, or autonomic related event of a brief
and episodic nature occurring in sleep. Usually
occur during REM sleep, such as eye movements and/or muscle twitches

Pulse
Oximetry - non-invasive measure of oxygen saturation; that is the amount
of oxygen saturated in the hemoglobin in terms of percentage; not as accurate as the values obtained from
an arterial blood gases (ABG) test and should only be used as a gauge of
oxygenation. Normal ranges are between
95-100%.

Quiet
Sleep - The term frequently used instead of NREM sleep
to describe the sleep of infants.

Radiofrequency
(RF) - Electromagnetic radiation in the frequency range 3 kilohertz
(kHz) to 300 gigahertz (GHz); considered to include microwaves and radio
waves. Microwaves occupy the spectral region between
300 GHz and 300 MHz, while RF or radio waves include 300 MHz to 3 kHz.

Radiofrequency
(RF) Procedure (also known as Somnoplasty) - procedure for treating
nasal obstruction, snoring and in some cases, sleep apnea. The procedure
uses radiowave energy to reduce snoring and the size of the soft palate.

REM
sleep, rapid eye movement sleep - sleep characterized by the active
brain waves, flitting motions of the eyes, and weakness of the muscles;
most dreaming occurs in this stage, which accounts for about 20% of sleep
in adults.

REM
Density - A function that expresses the frequency of eye movements per
unit of time during REM sleep.

REMS
latency - The period of time in the sleep period from sleep onset to
the first appearance of stage REMS.

REM
Motor Atonia - The active suppression of activity in the antigravity
and voluntary muscles during REM sleep. The muscles are completely flaccid
and limp.

REM
onset - designation for commencement of a REM period; used also as a shorthand term for a sleep-onset REM period

REM
period - REM portion of a NREM-REM cycle; early in the night it may
be as short as a half-minute, whereas in later cycles longer than an hour.

REM
rebound or recovery - lengthening and increase in frequency and density
of REM periods, which results in an increase in REM percent above base line.
REM rebound follows REM deprivation once the inhibitory influence is removed

REM
Sleep Behavior Disorder (RBD)- disorder in which REM motor atonia is
partially or completely absent and the individual acts out the ongoing dream.
The behavior in REM behavior disorder is often correlates with the ongoing,
hallucinatory REM dream episode.

REM
Sleep Episode - REM sleep portion of a NREM-REM sleep cycle. Early in
the first sleep period, episodes may be only several minutes in duration.
Later REM episodes almost are always longer, 20 to 30 minutes up to an hour.

REM
Sleep Intrusion - brief interval of REM sleep appearing out of its usual
positioning in the NREM-REM sleep cycle.

REM
Sleep Latency - interval from sleep onset to the first appearance of
REM sleep

REM
Sleep Onset - designation for the first epoch of a REM sleep episode

REM
Sleep Percent - proportion of total sleep time occupied by REM sleep

REM
Sleep Rebound - compensatory increase in REM sleep following experimental
reduction. Extension of time in, and an increase in frequency and density
of REM sleep episodes; usually an
increase in REM sleep percent of total sleep time above baseline values

Restless Legs Syndrome (RLS) - sleep
disorder characterized by a deep creeping, or crawling sensation in the
legs that tends to occur when an individual is not moving. There is an almost
irresistible urge to move the legs; the sensations are relieved by movement.

Shiftwork
- working hours outside of the conventional daytime hours of 9:00 a.m. to
5:00 p.m.

Sleep
- a state marked by lessened consciousness, lessened movement of the skeletal
muscles, and slowed-down metabolism

Sleep
Apnea - cessation of breathing for 10 or more seconds during sleep

Sleep
architecture - NREM/REM stage and cycle infrastructure of sleep understood
from the vantage point of the quantitative relationship of these components
to each other

Sleep
cycle - synonymous with NREM-REM cycle

Sleep
Debt - result of recurrent sleep deprivation which occurs over time
when an individual does not experience a sufficient amount of the restorative
daily sleep that is required to maintain a sense of feeling rested and refreshed.
.

Sleep
Deprivation - acute or chronic lack of sufficient sleep.

Sleep
Disorders - broad range of illnesses arising from many causes, including,
dysfunctional sleep mechanisms, abnormalities in physiological functions
during sleep, abnormalities of the biological clock, and sleep disturbances
that are induced by factors extrinsic to the sleep process

Sleep
efficiency (SE) - proportion of sleep in the period potentially filled
by sleep--ratio of total sleep time to time in bed

Sleep
Episode - interval of sleep that may be voluntary or involuntary

Sleep
Extension - extending sleep time by increasing the time in bed

Sleep
Fragmentation - brief arousals occurring throughout the night, reducing
the total amount of time spent in the deeper levels of sleep.

Sleep
hygiene - conditions and practices that promote continuous and effective
sleep, including regularity of bedtime and arise time; conforming time spent
in bed to the time necessary for sustained and individually adequate sleep
(i.e., the total sleep time sufficient to avoid sleepiness when awake); restriction of alcohol and caffeine beverages
in the period prior to bedtime; employment
of exercise, nutrition, and environmental factors so that they enhance,
not disturb, restful sleep

Sleep
Hyperhydrosis - excessive sweating during sleep.

Sleep
Inertia - feelings of grogginess and/or sleepiness that persist longer
than 10 to 20 minutes after waking up

Sleep
interruption - breaks in the sleep architecture resulting in arousal
and wakefulness

Sleep
latency - time period measured from "lights out," or bedtime,
to the beginning of sleep

Sleep
log (-diary) - daily, written record of an individual's sleep-wake pattern
containing such information as time of retiring and arising, time in bed,
estimated total sleep period, number and duration of sleep interruptions,
quality of sleep, daytime naps, use of medications or caffeine beverages,
nature of waking activities, and other data

Sleep
stage 2 - a stage of NREM sleep characterized by sleep spindles and
K complexes against a relatively low-voltage, mixed-frequency EEG background;
high-voltage delta waves may comprise up to 20% of stage 2 epochs; usually
accounts for 45-55% of total sleep time.

Sleep
stage 3 - a stage of NREM sleep defined by at least 20 and not more
than 50% of the period (30 second epoch) consisting of EEG waves less than
2 Hz and more than 75 uV (high -amplitude delta waves); a "delta"
sleep stage; with stage 4, it constitutes "deep "NREM sleep; appears usually only in the first third of the sleep period; usually
comprises 4-6% of total sleep time.

Sleep
stage 4 - all statements concerning
NREM stage 3 apply to stage 4 except that high-voltage, slow EEG waves,
cover 50% or more of the record; NREM
stage 4 usually takes up 12-15% of total sleep time.
Somnambulism, sleep terror, and sleep-related enuresis episodes generally
start in stage 4 or during arousals from this stage

Sleep stage REM - the stage of sleep
found in all mammal studies, including man, in which brain activity is extensive,
brain metabolism is increased, and vivid hallucinatory imagery, or dreaming
occurs (in humans). Also called "paradoxical sleep" because,
in the face of this intense excitation of the CNS and presence of spontaneous
rapid eye movements, resting muscle activity is suppressed. The EEG is
a low-voltage, fast-frequency, non alpha record. Stage REMS is usually
20-25% of total sleep time.

Sleep
structure - similar to sleep architecture.
Sleep structure, in addition to encompassing sleep stage and cycle
relationships, assesses the within-stage qualities of the EEG and other
physiological attributes.

Sleepiness
(somnolence, drowsiness) - difficulty in maintaining the wakeful state so
that the individual falls asleep if not actively kept aroused; not simply a feeling of physical tiredness or
listlessness

Sleep
talking - talking in sleep takes place during stage REMS, representing
a motor breakthrough of dream speech, or in the course of transitory arousals
from NREMS and other stages. Full
consciousness is not achieved and no memory of the event remains.

Sleepwalker
or Sleepwalking - individual subject to somnambulism (one who walks
while sleeping). Sleepwalking typically
occurs in the first third of the night during deep NREM sleep (stages 3
and 4).

Sleep-wake, 24 hour cycle - the clock
hour relationships of the major sleep and wake phases in the 24 hour cycle:
similar to sleep pattern.

Sleep-wake
shift (-change, -reversal) – sleep wholly or partially moved to a time
of customary waking activity, and the latter is moved to the habitual sleep
period; common in jet lag and shift work.

Sleep-Wake
Transition Disorder - disorder occuring during the transition from wakefulness
to sleep or from one sleep stage to another;
a form of parasomnia

Slow
wave sleep (SWS) - sleep stages 3 and 4

SmartPAP
(Smart CPAP) - (Smart [Continuous] Positive Airway Pressure) Medical
device used in the treatment of obstructive sleep apnea providing preset
levels of continuous airflow, and automatically adjusting to keep the breathing
passages open by sensing changes in airway integrity. The air flows from
the device through a tube that connects to a nose or face mask.

Snoring
- noise produced primarily with inspiratory respiration during sleep owing
to vibration of the soft palate and the pillars of the oropharyngeal inlet. Many snorers have incomplete obstruction of
the upper airway, and may develop obstructive sleep apnea.

Soft
Palate - membranous and muscular fold suspended from the posterior margin
of the hard palate and partially separating the oral cavity from the pharynx

Subwakefulness
syndrome - syndrome defined as a defect in the CNS support system for
waking. The few individuals reported
with subwakefulness syndrome have daytime drowsiness and daytime sleep episodes
that are always composed of NREMS stages 1 or 2. The naps occur repetitively

Sudden
Infant Death Syndrome (SIDS) - sudden
and unexpected death of an apparently healthy infant, whose death remains
unexplained after the performance of an adequate postmortem investigation. Death usually occurs during sleep. SIDS is a classification that is used to describe
a deceased infant. It is not a disease, nor can it be a diagnosis for a
living baby.

Synchronization
- chronobiological term used to indicate that two or more rhythms recur
with the same phase relationship. In
an EEG tracing, the term is used to indicate an increased amplitude with
an occasional decreased frequency of the dominant activities.

Synchrony
- scheduling sleep to synchronize with the biological clock

Tachycardia
- rapid heart rate, usually defined by a pulse rate of over 100 beats per
minute (bpm).

Thermocouples
- small devices placed near the nostrils or mouth to measure air flow by
sensing temperature changes; expired air is warmer than inspired air.

Thermoregulation
- regulation of body temperature in mammals.

Theta
waves - EEG activity with a frequency of 4-8 Hz

Thoracic
Excursion - thoracic (chest) movement, indicating respiratory effort. Usually measured by the placement of a sensor
band, which includes a strain gauge around the chest. The sensor band records chest wall movement
associated with respirations..

Tidal
Volume - amount of air that
passes in and out of the lungs in an ordinary breath;
usually expressed in liters

Tonsils
- pair of prominent masses of lymphoid tissue that are located opposite
each other in the throat between the anterior and posterior pillars of the
fauces (the narrow passage from the mouth to the pharynx situated between
the soft palate and the base of the tongue). Composed of lymph follicles
grouped around one or more deep crypts.

Tonsillectomy
- surgical removal of the tonsils

Total
Recording Time - duration of time from sleep onset to final awakening.
I n addition to total sleep time, it is comprised of the time taken up by
wake periods and movement time until wake-up.

Total
sleep period - period of time measured from sleep onset to final awakening.
In addition to total sleep time, it is comprised of the time taken up by
arousals and movement time until wake-up

Total
sleep time (TST) - amount of actual sleep time in a sleep period; equal
to total sleep period less movement and awake time. Total sleep time is the total of all REMS and NREMS in a sleep period.

Tracheotomy
- surgical procedure to create an opening in the trachea (windpipe) so that
one can breathe

Tracheostomy
- refers to the opening in the trachea. As a treatment for severe obstructive
sleep apnea, a tube to assist oxygenation and ventilation and/or to overcome
an obstruction in the airway located superiorly.

Transducer
- device designed to convert energy from one form to another

Transient
Arousals - brief awakenings from sleep

Transient
Insomnia - difficulty sleeping for only a few nights

Tricyclic
Antidepressants - medication for depression.
Most tricyclic antidepressants also reduce REM sleep; also used to control cataplectic attacks, hypnogogic
hallucinations, and sleep paralysis.

Turbinate
- small, shelf-like, cartilaginous structures covered by mucous membranes,
which protrude into the nasal airway to help warm, humidify, and cleanse
inhaled air on its way to the lungs.

Twilight
Zone - slang popular term to describe the waking state of individuals
whose MSLT scores are 5 minutes or less. Such individuals are usually sleep
deprived or suffer from a sleep disorder.

Twitch
(Body Twitch) - very small body movement such as a local foot or finger
jerk which is not usually associated with an arousal.

Unattended
CPAP Titration Study - sleep study that is usually performed in the
home, after determining that a patient has a sleep related breathing disorder
such as OSA or Upper Airway Resistance Syndrome, and is likely to benefit
from CPAP therapy.

Unintended
Sleep Episode - sleep episode that is not planned and may happen during
an activity in which such an episode is hazardous, such as when driving
a car or working with machinery

Upper
Airway - part of the respiratory anatomy that includes the nose, nostrils,
sinus passages, septum, turbinates; the
tongue, jaws, hard and soft palate, muscles of the tongue and throat, etc.

Upper
Airway Resistance Syndrome (UARS) - part of the spectrum of obstructive
sleep-related breathing disorders in which repetitive increases in resistance
to airflow in the upper airway lead to brief arousals and daytime fatigue. Apneas and hypopneas (see RDI) may be totally
absent. Blood oxygen levels can
be in the normal range.

Uvula
- small soft structure hanging from the bottom of the soft palate in the
midline above the back of the tongue.

Uvulopalatopharyngoplasty
(UPPP) - also abbreviated as UPP or UP3 this operation is performed
on the throat to treat snoring and sleep apnea.
UPPP is an accepted means of surgical treatment has a curative rate
of less than 50%. Scientific evidence
suggests that UPPP works best in retropalatal and combination retropalatal
and retrolingual obstruction

Wake
time - total
time that is scored awake in a polysomnogram occurring between sleep onset
and final wake-up

White
Noise - mixture of sound waves extending over a wide frequency range
that may be used to mask unwanted noise that may interfere with sleep

Wilkinson
Addition Test - performance test; numbers
added for one hour. Often included in a battery of tests to measure the
impact of acute or chronic sleep loss.

Zeitgeber- environmental time cue that entrains biological rhythms to a specific
periodicity. Known Zeitgebers are
light, melatonin and physical activity.
To be effective, these signals must occur when the biological clock
is in a responsive phase.